The present invention relates to a tibial portion of a knee joint endoprosthesis with a securing shank to be inserted into the medullar cavity of the tibia, which, on one end, is provided with or is without a tibia condyle terminal or closing plate for the attachment of the articular parts of the prosthesis.
From the DE-A-36 27 097, a shank that is insertable into the medullar space of a bone for articular endoprostheses is known, which, over at least a part of its length, is constructed so as to be hollow and is provided with at least one longitudinal slot which terminates in the cavity and forms a connection of the cavity with the surrounding area. Due to such a construction of a securing shank for articular endoprostheses, it is intended to approximate their natural resilience to that of the natural bone.
An endoprosthesis for a knee joint, comprising a tibial portion to be secured by means of a shank with a central web and with gliding surfaces disposed on both sides of the latter, and a femoral portion to be likewise secured by means of a shank which is provided with two skids that bridge the web and are supported on the gliding surfaces, wherein the tibial and the femoral portions are movably interconnected by means of a pivot located transversally to the web eccentrically to the tibia shank, is known from the DE-A-25 49 819. In this endoprosthesis, the pivot is movably inserted eccentrically against the convexity of the gliding surface toward the rear in the web in its longitudinal axis, while the ends of the pivot engage with play into guide grooves in the skids extending roughly parallelly to the lower skid surface and which are open toward the top, whereas the web and the spacing of the skids toward the rear are constructed so as to become wider in a manner known per se. Accordingly, this endoprosthesis of a knee joint is constructed in such a way that the articular movements of a natural knee joint are retained or very nearly retained, the femoral portion being able during the bending procedure to lengthen rearwardly in a rolling and gliding manner to an extent which differs from case to case and, in the process, also allows a rotary movement of the thighs relative to each other to take place.
A securing shank for a tibial portion of a knee joint endoprosthesis connected or to be connected to it, which, over its length, possesses a constant or, in the direction of its free end, a conically narrowing cross-sectional course, is known from the DE-A-26 60 458. In this shank, the longitudinal portion engaging into the medullar cavity, at least over a part of the shank length, has a cross-sectional configuration in the form of an irregular triangle with rounded edges and outwardly curved sides. On account of such a shank construction, a torsionally safe position of the tibial portion with very slight play is possible which, over and above that, corresponds to the position of the natural tibial tabula.
In comparison with the known securing shanks for knee joint endoprostheses, it is the object of the present invention to provide a tibial portion for a light-weight securing means which meets the biomechanical requirements of a knee joint endoprosthesis in the tibial bone with the possibility of achieving a vascularization of the blood vessels in the bone up to the medullar cavity, in which, moreover, the tibial portion has to possess large areas for absorbing flexural forces.